Colorectal cancer (CRC) is a malignant disease that affects millions of people around the world. The major cause of patient death is by tumor metastasis. Thus, studying CRC metastasis is critically important not only for understanding mechanisms of tumor malignancy, but also for developing tools for early diagnosis and effective treatment. Metastasis of CRC emerges from multiple genetic alterations and cellular disorganization. It occurs in a phase of tumor progression by metastatic variant cells that possess invasive activities characterized by increased cell migration, tissue invasion, and organ colonization. Despite intensive studies, our knowledge about the nature of invasive cells and the mechanisms underlying their origination is still limited. Recent studies using DNA microarray analysis have revealed that the proclivity of CRC metastasis is acquired early during multistage tumorigenesis. It is manifested only at late stages aided with additional genetic aberrations or cellular disorganization. During the study of CRC progression towards malignancy, we found that splicing variants of the RON receptor tyrosine kinase, such as oncogenic RON160, play a critical role in priming CRC cells with metastatic capability. Increased RON160 expression in colonic cells not only mediates cell transformation, but also promotes malignant metastasis. Thus, RON160 seems to act as a regulated metastasis-promoting switch in CRC cells. The goal of this project is to determine the signaling mechanisms by which oncogenic RON variants regulate metastatic phenotypes of CRC cells. We believe that malignancy acquired by metastatic variants of CRC cells is determined by metastasis-related proteins including oncogenic RON160. We hypothesize that splicing RON variants, such as oncogenic RON160, have the priming effect on CRC cells resulting in increased metastatic capabilities. In other words, metastatic potential is driven by oncogenic RON variants that initiate and activate cellular motile/invasive machinery leading to metastatic processes. To test this hypothesis, our studies will focus on following three specific aims: 1) To study how oncogenic RON160 is expressed in primary and metastatic CRC samples and its role in priming CRC cells into highly malignant variants; 2) To determine the roles of RON160-activated signaling proteins and underlying mechanisms required for malignant conversion of CRC cells; and 3) To validate RON160 as a therapeutical target using monoclonal antibodies (mAbs) that exhibit growth-inhibitory and apoptotic effects on CRC cells. This work is important for the following reasons. First, it will determine the importance of RON160 in the progression of CRC cells towards malignancy. Second, it will facilitate our understanding of mechanisms underlying CRC metastasis. Finally, this work may identify novel targets for drug development to treat metastatic CRC. PUBLIC HEALTH RELEVANE: Metastasis of colon cancer is the ultimate cause of patient death. Currently, our knowledge about tumor metastasis is very limited, which reflects the lack of effective treatment for this deadly disease at clinical practice. Thus, understanding how colon cancer metastasizes is critically important. The project in this grant application is to determine the role of a cellular protein called RON in colon cancer metastasis. It is believed that such studies will help to determine mechanisms underlying colon cancer metastasis, to identify novel metastatic markers for early diagnosis, and to develop new drugs to treat patients with metastatic colon cancer.